This invention relates generally to materials for making medical grade products, and more particularly concerns coextruded flexible multilayer medical polyvinyl chloride (PVC) tubing with inner and outer layers coextruded with different plasticizers to provide the tubing with improved bonding properties, and to limit migration of a plasticizer in an outer layer to the inside of the tubing to minimize contact of the plasticizer with patient fluids, drugs or therapeutic agents carried in the tubing.
In the modem medical industry, medical grade tubing is commonly used to carry bodily fluids to and from patients such as in renal or blood therapies, and for delivering various drugs and therapeutic agents to patients. Such medical grade tubing is also useful in carrying patient specimens, carrier fluids and analytical agents in medical apparatus or apparatus used for medical analysis. Plastic materials are useful in forming medical grade tubing because the characteristics of the tubing can be adapted by appropriate formulation of the plastic material forming the tubing, and formation of the tubing with multiple layers having different characteristics that contribute to the desired overall characteristics of the tubing. In the formulation and construction of such medical grade tubing, it is important that such tubing be capable of being bonded with y-sites, burettes, and other devices. Other properties that may be desirable for medical grade tubing include flexibility, clarity, durability, heat resistance, strength, and the ability to shield the interior lumen of the tubing from radio waves, light or other radiation such as X-rays.
Flexible medical grade polyvinyl chloride (PVC) tubing is widely utilized due to its generally good flexibility, clarity, ease of assembly with solvent bonding, relatively low cost, and the ease of manufacturing such tubing with varying wall thicknesses and inside diameters to suit a variety of medical devices. Varying the amounts of plasticizer in the PVC formulation can be used to change the durometer or hardness and flexibility of the PVC tubing for specific applications. For example, softer, more flexible tubing can be useful in connection with parenteral infusion applications, while high durometer, less flexible, more durable PVC tubing can be more suitable for monitoring lines and medical equipment. However, some additives which contribute such desirable properties to the plastic material of the tubing may migrate from the plastic medical tubing, which may become a concern when patient bodily fluids, drugs or therapeutic agents are in contact with the tubing, such as in chronic renal dialysis when there is prolonged contact of tubing with circulating blood.
Various types of flexible, plastic, multilayer medical grade tubing are known which contain different compounds on the outside and inside of the tubing. One type of flexible medical tubing includes a coextruded multilayer medical grade tubing having an outer layer containing a polypropylene copolymer and a core formed from PVC plasticized with di-ethylhexyl phthalate (DEHP, also known as dioctyl phthalate or DOP). However, polypropylene copolymer is crystalline and difficult to solvent bond to y-sites, burettes and other devices, and migration of DEHP plasticizer from the core of the tubing can occur.
Another type of medical tubing has multiple layers formed from a soft set PVC, with a physiologically unobjectionable wall, and an adjacent physiologically questionable wall containing one or more physiologically questionable and/or untested additives. The physiologically questionable or untested additive may be one or more radiation absorbing substances which tend to migrate. This tendency to migrate is counteracted by providing a gradient of a plasticizer or softener substance such as DEHP or di-ethylhexyl adipate (DEHA, also known as dioctyl adipate, or DOA) from the physiologically unobjectionable wall to the physiologically questionable wall, which prevents migration of the questionable additive. The outer jacket of the tube of PVC is formed with a lesser amount of the plasticizer, and the inner layer of the tubing of PVC is formed with a greater amount of the plasticizer. Such a plasticizer gradient between two layers of PVC is undesirable because it makes one layer softer than the other, and can cause the tubing to peel apart or kink. With a greater amount of plasticizer in the inner jacket of the tubing, the inner jacket becomes softer, so that the inner softer jacket of the tubing can become thinned, pinched, or cut through when the tubing is pinched, for example with a pinch type clamp such as a C-clamp.
While PVC with DEHP plasticizer is readily bondable to y-sites, burettes and other devices, it may be desirable to limit direct contact of DEHP with patient fluids, drugs or therapeutic agents. While DEHA can be used as a PVC plasticizer, it is difficult to bond PVC with DEHA plasticizer to other devices, so that stronger solvents are required to attain bonding of such tubing with other devices, which is undesirable. DEHA also chemically reacts with styrene based materials, such as polystyrene, so that bonding of PVC with DEHA plasticizer can eventually result in bond failure, because the DEHA can weaken the styrene material as well as the bonded joint over time.
One type of medical grade tubing has a multilayer structure not containing PVC, avoiding the use of any PVC plasticizers altogether. However, since PVC has proved to be such an extremely versatile and useful plastic, it would be desirable to provide a flexible medical grade PVC tubing utilizing DEHP, which is a useful and otherwise desirable PVC plasticizer, in a configuration that would limit migration and direct contact of DEHP with patient fluids, drugs or therapeutic agents, and that provides improved bonding properties to the flexible medical grade PVC tubing. The present invention meets these and other needs.
Briefly, and in general terms, the present invention provides for a flexible medical grade PVC tubing with inner and outer layers coextruded with different plasticizers to provide improved bonding properties to the tubing, and limited migration of plasticizer in an outer layer of the tubing to the inside of the tubing. The flexible medical grade PVC tubing is useful for carrying fluids, drugs and therapeutic agents.
The present invention accordingly provides for a flexible medical grade tubing having coextruded first and second layers. The first layer is formed of PVC containing a first plasticizer, and forms an innermost layer of the tubing. The second layer surrounds the first layer, and is formed of PVC containing a second plasticizer different from the first plasticizer. The second plasticizer in the second layer provides valuable properties to the characteristics of the tubing, and the first layer with the first plasticizer limits migration of the second plasticizer to the inside of the tubing. In a presently preferred embodiment, the first layer can be dimensioned to have a thickness sufficient to limit migration of the second plasticizer to the inside of the tubing to a desired level. In a presently preferred embodiment, the first plasticizer is di-ethylhexyl adipate (DEHA). The second plasticizer is preferably a plasticizer that contributes desired characteristics and improved bonding properties to the medical tubing. In one presently preferred embodiment, the second plasticizer is di-ethylhexyl phthalate (DEHP).
In a presently preferred embodiment, the second layer forms the outermost layer of the tubing. In an alternate embodiment, the flexible medical grade tubing can optionally include a third layer surrounding the second layer and containing a plasticizer different from the second plasticizer, such as di-ethylhexyl adipate (DEHA). The third layer can have a thickness dimensioned sufficient to limit migration of the second plasticizer to the outside of the tubing to a desired level. The third layer can optionally form the outermost layer of the tubing.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.